Process for Producing Ethylene Oxide from Ethane by Oxidative Dehydrogenation and Epoxidation with Split Recycle

ABSTRACT

An ethylene oxide (EO) production process comprising (a) introducing a first reactant mixture (C2H6, O2) to a first reactor to produce a first effluent stream (C2H4, C2H6, O2); (b) introducing a second reactant mixture to a second reactor to produce a second effluent stream (EO, C2H4, C2H6, O2); wherein the second reactant mixture comprises at least a portion of first effluent stream; (c) separating the second effluent stream into an EO product stream (EO) and recycle stream (C2H4, C2H6, O2); wherein ethylene is not separated from recycle stream and/or first effluent stream; and (d) recycling a first portion of recycle stream to the first reactor, and a second portion of recycle stream to the second reactor; wherein recycle split ratio &lt;0.6; and wherein recycle split ratio is defined as ratio of volumetric flowrate of first portion of recycle stream divided by the sum of volumetric flowrates of first portion and second portion of recycle stream.

CROSS REFERENCE TO RELATED APPLICATION

This application is a filing under 35 U.S.C. 371 of InternationalApplication No. PCT/US2021/021174 filed Mar. 5, 2021, entitled “Processfor Producing Ethylene Oxide from Ethane by Oxidative Dehydrogenationand Epoxidation with Split Recycle,” which claims priority to U.S.Provisional Application No. 62/987,176 filed Mar. 9, 2020, whichapplications are incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present disclosure relates to a process for the production ofethylene oxide, more specifically a process for the production ofethylene oxide that integrates oxidative dehydrogenation of ethane withethylene epoxidation.

BACKGROUND

Ethylene oxide (EO) is an important petrochemical intermediate, and itis a starting material for the production of ethylene glycol, as well asother glycols (e.g., polyethylene glycols), ethoxylates, ethanol-amines,solvents, and glycol ethers. EO is currently produced using a sequenceof conventional ethylene production technology (e.g., steam cracking,such as ethane steam cracking) and conventional ethylene oxideproduction technology (e.g., catalytic epoxidation). Steam cracking is acapital-intensive process with incomplete selectivity to ethylene.

Ethane oxidative dehydrogenation (ODH) technology has been contemplatedfor the production of ethylene with subsequently using the producedethylene to yield EO, but such a process has not yet found significantcommercial application. Subsequent to the recovery of the EO, the streamcontaining unconverted ethylene and ethane could be separated into anethane-rich stream that could be recycled to the ODH reactor and anethylene-rich stream that can be recycled to the EO reactor, but suchseparation is very costly, owing in part to the large stream volume thatwould need to undergo the separation. Further, such a separation wouldbe conventionally carried out by cryogenic distillation; and undertakinga large-scale cryogenic separation of the stream containing unconvertedethylene and ethane obtained after the recovery of EO, given associatedrefrigeration loads and distillation tower sizes, would be prohibitivelyexpensive. Thus, there is an ongoing need for the development ofprocesses that combine the ODH and EO technologies, while providing foran increased chemical efficiency and/or lower capital cost.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the preferred embodiments of the disclosedmethods, reference will now be made to the accompanying drawing inwhich:

FIG. 1 displays a schematic of a system for an ethylene oxide (EO)production process; and

FIG. 2 displays another schematic of a system for an EO productionprocess.

DETAILED DESCRIPTION

Disclosed herein are processes for producing ethylene oxide (EO)comprising using (i) a first catalytic reactor (e.g., oxidativedehydrogenation (ODH) reactor) for converting ethane to ethylene by ODHand (ii) a second catalytic reactor (e.g., EO reactor) for convertingethylene to EO. The processes for producing EO as disclosed herein canadvantageously provide for higher overall carbon efficiency and/or loweroverall capital intensity than conventional processes for the productionof EO, for example a conventional process employing an ethane steamcracker combined with an EO reactor. The processes for producing EO asdisclosed herein can advantageously provide for configurations ofsystems for EO production that enhance capital efficiency and/or carbonefficiency of an integrated process (i.e., a process that integrates ODHand EO technologies) that converts an ethane feedstock to EO, whereinthe produced EO can be subsequently converted to ethylene glycol. TheODH and EO reactors as disclosed herein can be advantageously operatedin a recycle configuration, wherein substantially all of the effluentfrom the ODH reactor can be directed to the EO reactor, and wherein theunreacted part of the effluent from the EO reactor (i.e., after EOrecovery) can be recycled partly to the ODH reactor and partly to the EOreactor. In this recycle process (i.e., the process for producing EO asdisclosed herein), there is no need to separate of ethylene from ethanein the unreacted part of the effluent from the EO reactor. Further,there is substantially no need to separate unconverted oxygen in theprocess, since oxygen is conveniently and advantageously recycled backto the ODH and EO reactors.

The processes for producing EO as disclosed herein advantageouslyrecycle a significant portion (e.g., greater than about 40%) of therecycle flow (i.e., unreacted part of the effluent from the EO reactor)to the EO reactor, wherein a smaller portion of the recycle flow isreturned to the ODH reactor. The processes for producing EO as disclosedherein can advantageously introduce oxygen make-up streams to each ofthe ODH reactor and the EO reactor. Further, the processes for producingEO as disclosed herein can advantageously control process performance byvarying the recycle split ratio (i.e., the split ratio of the recycleflow between the ODH and the EO reactors).

Other than in the operating examples or where otherwise indicated, allnumbers or expressions referring to quantities of ingredients, reactionconditions, and the like, used in the specification and claims are to beunderstood as modified in all instances by the term “about.” Variousnumerical ranges are disclosed herein. Because these ranges arecontinuous, they include every value between the minimum and maximumvalues. The endpoints of all ranges reciting the same characteristic orcomponent are independently combinable and inclusive of the recitedendpoint. Unless expressly indicated otherwise, the various numericalranges specified in this application are approximations. The term “frommore than 0 to an amount” means that the named component is present insome amount more than 0, and up to and including the higher namedamount.

The terms “a,” “an,” and “the” do not denote a limitation of quantity,but rather denote the presence of at least one of the referenced item.As used herein the singular forms “a,” “an,” and “the” include pluralreferents.

As used herein, “combinations thereof” is inclusive of one or more ofthe recited elements, optionally together with a like element notrecited, e.g., inclusive of a combination of one or more of the namedcomponents, optionally with one or more other components notspecifically named that have essentially the same function. As usedherein, the term “combination” is inclusive of blends, mixtures, alloys,reaction products, and the like.

Reference throughout the specification to “an aspect,” “another aspect,”“other aspects,” “some aspects,” and so forth, means that a particularelement (e.g., feature, structure, property, and/or characteristic)described in connection with the aspect is included in at least anaspect described herein, and may or may not be present in other aspects.In addition, it is to be understood that the described element(s) can becombined in any suitable manner in the various aspects.

As used herein, the terms “inhibiting” or “reducing” or “preventing” or“avoiding” or any variation of these terms, include any measurabledecrease or complete inhibition to achieve a desired result.

As used herein, the term “effective,” means adequate to accomplish adesired, expected, or intended result.

As used herein, the terms “comprising” (and any form of comprising, suchas “comprise” and “comprises”), “having” (and any form of having, suchas “have” and “has”), “including” (and any form of including, such as“include” and “includes”) or “containing” (and any form of containing,such as “contain” and “contains”) are inclusive or open-ended and do notexclude additional, unrecited elements or method steps.

For purposes of the disclosure herein, the term “reactor” is understoodto encompass one or more reaction zones; one or more reaction stages;one or more reaction vessels; or combinations thereof.

Unless defined otherwise, technical and scientific terms used hereinhave the same meaning as is commonly understood by one of skill in theart.

Referring to the configuration of FIG. 1 , an ethylene oxide (EO)production system 100 is disclosed. EO production system 100 generallycomprises a first reactor or an oxidative dehydrogenation (ODH) reactor1; a second reactor or an EO reactor 2; a product recovery system 3; anda carbon dioxide (CO₂) removal system 4.

Referring to the configuration of FIG. 2 , an ethylene oxide (EO)production system 200 is disclosed. EO production system 200 generallycomprises a first reactor or an ODH reactor 1; a second reactor or an EOreactor 2; a product recovery system 3; and a CO₂ removal system 4. Aswill be appreciated by one of skill in the art, and with the help ofthis disclosure, EO production system components shown in FIGS. 1-2 canbe in fluid communication with each other (as represented by theconnecting lines indicating a direction of fluid flow) through anysuitable conduits (e.g., pipes, streams, etc.). Further, and as will beappreciated by one of skill in the art, and with the help of thisdisclosure, EO production systems 100 and 200 depicted in FIGS. 1-2 mayfurther comprise additional operations and/or equipment, such ascompressors, heaters, coolers, water removal systems, etc. Commonreference numerals refer to common components present in one or more ofthe Figures, and the description of a particular component is generallyapplicable across respective Figures wherein the component is present,except as otherwise indicated herein.

In an aspect, a process for producing EO as disclosed herein cancomprise a step of introducing a first reactant mixture (e.g., ODHreactor feed stream 5) to the ODH reactor 1 to produce a first effluentstream (e.g., ODH reactor effluent stream 6); wherein the first reactantmixture comprises ethane (C₂H₆), and oxygen (O₂); and wherein the firsteffluent stream comprises ethylene (C₂H₄), ethane, and oxygen. The firstreactant mixture further comprises ethylene, wherein the mole fractionof ethylene in the first effluent stream is greater than the molefraction of ethylene in the first reactant mixture. In some aspects,ethane, ethylene and oxygen may be fed to the ODH reactor 1 together,for example via ODH reactor feed stream 5, as displayed in theconfiguration of FIGS. 1 and 2 . In other aspects, ethane, ethylene andoxygen may be fed to the ODH reactor 1 separately, wherein one or morecomponents of the first reactant mixture may be fed to the ODH reactor 1separately. For example, a stream comprising ethylene and ethane and aseparate stream comprising oxygen may be fed to the ODH reactor 1separately (e.g., without contacting each other prior to introducing tothe ODH reactor 1).

In some aspects, for example as displayed in the configuration of FIGS.1-2 , a recycle stream (e.g., ODH recycle feed stream 16) recovered fromthe EO production process may be combined with one or more streams toproduce the ODH reactor feed stream 5. For example, ODH recycle feedstream 16 may be combined with an ethane feed stream 17, an ODH oxygenmake-up feed stream 18, and optionally with a ballast gas make-up stream19 to yield the ODH reactor feed stream 5. ODH recycle feed stream 16comprises ethylene, ethane, oxygen, and a ballast gas, and it will bedescribed in more detail later herein. Ethane feed stream 17 providesfor supplemental ethane or “fresh” ethane, which replenishes the ethanethat has been consumed (e.g., via ODH reaction in reactor 1, undesiredside reactions in EO reactor 2) and/or lost (e.g., via purge stream 13)in the process. For purposes of the disclosure herein, the term “fresh”component (e.g., fresh ethane, fresh oxygen, fresh methane, etc.) refersto a component of a reactant mixture (e.g., first reactant mixture,second reactant mixture, etc.) that does not comprise the componentrecovered from the process and recycled back into the process, butrather refers to a supplemental source of such component which isintroduced to the reactant mixture.

In some aspects, the first reactant mixture can be characterized by amolar ratio of ethylene to ethane of equal to or greater than about 1.3,equal to or greater than about 1.5, equal to or greater than about 2.0,equal to or greater than about 2.1, equal to or greater than about 2.2,equal to or greater than about 2.3, equal to or greater than about 2.4,or equal to or greater than about 2.5, from about 1.3 to about 3.0, fromabout 1.5 to about 2.7, or from about 2.0 to about 2.6. In otheraspects, the first reactant mixture can be characterized by a molarratio of ethylene to ethane of less than about 1.3, less than about 1.0,or less than about 0.5, from about 0.1 to less than about 1.3, fromabout 0.2 to about 1.0, or from about 0.3 to about 0.8.

In an aspect, the ODH oxygen make-up feed stream 18 can be provided tothe ODH reactor 1. Stream 18 can be oxygen gas, technical oxygen (whichcan contain some air), air, oxygen enriched air, and the like, orcombinations thereof. In an aspect, stream 18 comprises substantiallypure oxygen (e.g., oxygen having less than about 1 vol. % contaminants,such as nitrogen (N₂), argon (Ar), etc.). The ODH oxygen make-up feedstream 18 provides for supplemental oxygen or fresh oxygen, whichreplenishes the oxygen that has been consumed (e.g., via ODH reaction inreactor 1, EO reaction in EO reactor 2, combustion reactions in reactors1 and 2, etc.) and/or lost (e.g., via purge stream 13) in the process.

In an aspect, the ballast gas make-up stream 19 can be provided to theODH reactor 1. Generally the term “ballast gas” refers to a diluent gas(e.g., gaseous compound or combination of gaseous compounds) that isintroduced to a particular reactor, wherein the diluent gas does notsignificantly participate in chemical reactions in that particularreactor. Ballast gases can be used for the purposes of diluting reactingcomponents in a reactor feed, providing better chemical and/or thermalcontrol of a reactor, etc.

Nonlimiting examples of ballast gases suitable for use in the presentdisclosure include methane (CH₄), N₂, steam, noble gases, such as Ar,and the like, or combinations thereof. In an aspect, the ballast gasmake-up stream 19 comprises methane.

The ODH reactor 1 can be any suitable reactor, such as a continuous flowreactor, a fixed bed reactor, a fluidized bed reactor, and the like, orcombinations thereof. In an aspect, the ODH reactor 1 comprises acontinuous flow fixed bed reactor.

In an aspect, the ODH reactor 1 can be characterized by an ODH reactoroperating temperature of from about 240° C. to about 400° C., from about250° C. to about 375° C., from about 260° C. to about 350° C., or fromabout 270° C. to about 340° C. The ODH reactor operating temperature isdefined as the average of ODH reactor inlet temperature and ODH reactoroutlet temperature. For purposes of the disclosure herein, the term“inlet temperature” (e.g., reactor inlet temperature) refers to thetemperature of the feed gas (e.g., first reactant mixture; secondreactant mixture) at the point it first comes into contact with thecatalyst (e.g., ODH catalyst; EO catalyst), which inlet temperature maybe higher than the temperature of fresh feed introduced into thereactor, for example because the feed has been preheated within thereactor. Further, for purposes of the disclosure herein, the term“outlet temperature” (e.g., reactor outlet temperature) refers to thetemperature of the effluent at the outlet out of the reactor.

In an aspect, the ODH reactor 1 can be characterized by an ODH reactoroperating pressure of from about 1 barg to about 35 barg, from about 3barg to about 30 barg, from about 5 barg to about 25 barg, or from about10 barg to about 20 barg. The ODH reactor operating pressure can besubstantially the same as an EO reactor operating pressure. In someaspects, the ODH reactor operating pressure can be from about 1 barg toabout 10 barg greater than the EO reactor operating pressure, therebyavoiding the need for excessive compression.

In an aspect, the ODH reactor 1 comprises an ODH catalyst. The ODHcatalyst comprises any ODH catalyst suitable for catalyzing an ODHreaction. For example, the ODH catalyst can comprise a mixed metaloxide, such as a mixed metal oxide comprising molybdenum, vanadium,niobium, tellurium, and the like, or combinations thereof. The ODHreactor, ODH catalyst, and ODH operating conditions (e.g., pressure,temperature) are described in more detail in U.S. Pat. Nos. 8,105,971;8,519,210; 8,846,996; and 9,545,610; each of which is incorporated byreference herein in its entirety.

The ethane introduced to the ODH reactor 1 contacts the ODH catalystand, in the presence of oxygen, is converted to ethylene via the ODHreaction (1):

C₂H₆+½O₂→C₂H₄+H₂O  (1)

Several side reactions or unwanted reactions (i.e., reactions other thanethane conversion to ethylene via the ODH reaction) can take place inthe ODH reactor 1, as follows. A portion of the ethylene, as well as aportion of the ethane in the ODH reactor 1 can be converted tooxygenated organic compounds, such as aldehydes and/or carboxylic acids;acetylene; carbon dioxide (CO₂); optionally carbon monoxide (CO); water;and the like; or combinations thereof.

In an aspect, the ODH reactor 1 can be characterized by an oxygenconversion of equal to or greater than about 30%, equal to or greaterthan about 45%, or equal to or greater than about 60%, from about 30% toabout 100%, from about 45% to about 100%, from about 45% to about 99%,or from about 60% to about 97.5%.

In an aspect, the ODH reactor 1 can be characterized by an ethaneconversion of equal to or greater than about 60%, equal to or greaterthan about 65%, equal to or greater than about 70%, equal to or greaterthan about 75%, equal to or greater than about 80%, equal to or greaterthan about 85%, or equal to or greater than about 90%; from about 60% toabout 100%, from about 65% to about 99.9%, from about 70% to about99.5%, from about 75% to about 99%, from about 80% to about 98.5%, fromabout 85% to about 98%, or from about 90% to about 97.5%.

In an aspect, the ODH reactor 1 can be characterized by an ethaneconversion of equal to or greater than about 70%. For example, the ODHreactor 1 can be characterized by an ethane conversion of equal to orgreater than about 70%, equal to or greater than about 75%, equal to orgreater than about 80%, equal to or greater than about 85%, or equal toor greater than about 90%; from about 70% to about 100%, from about 75%to about 99%, from about 80% to about 98.5%, from about 85% to about98%, or from about 90% to about 97.5%.

The ODH reactor effluent stream 6 can be recovered from the ODH reactor1, wherein the ODH reactor effluent stream 6 can comprise ethylene,ethane, oxygen, carbon dioxide, and water. The ODH reactor effluentstream 6 can further comprise the ballast gas (e.g., methane), andoptionally acetic acid, acetylene, CO, or combinations thereof. In anaspect, ethylene is not separated from the ODH reactor effluent stream6; i.e., ethylene is not separated from the ethane in the ODH reactoreffluent stream 6, prior to introducing the ethylene in the ODH reactoreffluent stream 6 into the EO reactor 2.

In an aspect, the ODH reactor effluent stream 6 can be characterized byan ethane concentration of less than about 30 mol %, less than about 25mol %, less than about 20 mol %, less than about 15 mol %, less thanabout 10 mol %, less than about 7.5 mol %, less than about 5 mol %, lessthan about 4 mol %, less than about 3 mol %, less than about 2 mol %, orless than about 1 mol %; from about 0.01 mol % to about 30 mol %, fromabout 0.02 mol % to about 25 mol %, from about 0.03 mol % to about 20mol %, from about 0.04 mol % to about 15 mol %, from about 0.05 mol % toabout 10 mol %, from about 0.07 mol % to about 7.5 mol %, or from about0.1 mol % to about 5 mol %.

In an aspect, the ODH reactor effluent stream 6 can be characterized byan ethane concentration of less than about 5 mol %, or from about 0.1mol % to about 5 mol %. For example, the ODH reactor effluent stream 6can be characterized by an ethane concentration of less than about 5 mol%, less than about 4 mol %, less than about 3 mol %, less than about 2mol %, or less than about 1 mol %; from about 0.1 mol % to about 5 mol%, from about 0.15 mol % to about 4 mol %, from about 0.2 mol % to about3 mol %, from about 0.25 mol % to about 2 mol %, or from about 0.3 mol %to about 1 mol %.

Although ethane is not separated from the ethylene in the ODH reactoreffluent stream 6, at least a portion of components other than ethylene,ethane, and oxygen may be separated from (e.g., removed from) ODHreactor effluent stream 6, prior to introducing the ethylene, ethane,and oxygen in the ODH reactor effluent stream 6 into the EO reactor 2.

In an aspect, at least a portion of the water and at least a portion ofthe acetic acid (if acetic acid is formed in the ODH reactor 1) can beremoved from the ODH reactor effluent stream 6, for example bycondensation (e.g., lowering the stream temperature to promotecondensation), to yield a dehydrated ODH reactor effluent stream.

In an aspect, at least a portion of the carbon dioxide can be removedfrom the ODH reactor effluent stream 6 and/or dehydrated ODH reactoreffluent stream to yield a CO₂-depleted ODH reactor effluent stream 20,for example as displayed in the configuration of FIG. 2 .

Referring to the configuration of FIG. 2 , the ODH reactor effluentstream 6 and/or dehydrated ODH reactor effluent stream can be combinedwith one or more streams (e.g., a recycle stream, such as EO recyclefeed stream 15; an EO oxygen make-up feed stream 14; optionally with aballast gas make-up stream) to produce the EO reactor feed stream 7,wherein at least a portion of the EO reactor feed stream 7 can besubjected to CO₂ removal in the CO₂ removal system 4 prior tointroducing to the EO reactor 2; and wherein the CO₂-depleted ODHreactor effluent stream 20 can be recovered from the CO₂ removal system4 and introduced to the EO reactor 2. The CO₂ removal system 4 mayemploy any suitable carbon dioxide removal technology, such as amine,caustic, carbonate-based absorption, and the like, or combinationsthereof. The CO₂-depleted ODH reactor effluent stream 20 may stillcontain CO₂, although at least 25 mol %, at least 35 mol %, at least 50mol %, or at least 70 mol % of the CO₂ in the ODH reactor effluentstream 6 and/or dehydrated ODH reactor effluent stream is removed in theCO₂ removal system 4.

In an aspect, a process for producing EO as disclosed herein cancomprise a step of introducing a second reactant mixture (e.g., EOreactor feed stream 7; CO₂-depleted ODH reactor effluent stream 20) tothe EO reactor 2 to produce a second effluent stream (e.g., EO reactoreffluent stream 8); wherein the second reactant mixture comprises atleast a portion of the first effluent stream; and wherein the secondeffluent stream comprises EO, ethane, ethylene, and oxygen.

In some aspects, for example as displayed in the configuration of FIGS.1-2 , the ODH reactor effluent stream 6 and/or dehydrated ODH reactoreffluent stream may be combined with one or more streams to produce theEO reactor feed stream 7. For example, the ODH reactor effluent stream 6and/or dehydrated ODH reactor effluent stream may be combined with arecycle stream (e.g., EO recycle feed stream 15), an EO oxygen make-upfeed stream 14, and optionally with a ballast gas make-up stream toproduce the EO reactor feed stream 7. EO recycle feed stream 15 hassubstantially the same composition as the ODH recycle feed stream 16.

In an aspect, the second reactant mixture (e.g., EO reactor feed stream7; CO₂-depleted ODH reactor effluent stream 20) can be characterized byan ethane concentration of less than about 30 mol %, less than about 25mol %, less than about 20 mol %, less than about 15 mol %, less thanabout 10 mol %, less than about 9 mol %, less than about 8 mol %, lessthan about 7 mol %, less than about 6 mol %, less than about 5 mol %,less than about 4 mol %, less than about 3 mol %, less than about 2 mol%, or less than about 1 mol %; from about 0.01 mol % to about 30 mol %,from about 0.01 mol % to about 25 mol %, from about 0.01 mol % to about20 mol %, from about 0.01 mol % to about 15 mol %, from about 0.01 mol %to about 10 mol %, from about 0.02 mol % to about 9 mol %, from about0.05 mol % to about 8 mol %, from about 0.06 mol % to about 7 mol %,from about 0.08 mol % to about 6 mol %, from about 0.1 mol % to about 5mol %, from about 0.1 mol % to about 4 mol %, from about 0.1 mol % toabout 3 mol %, from about 0.15 mol % to about 2 mol %, or from about 0.2mol % to about 1 mol %. In an aspect, the second reactant mixture (e.g.,EO reactor feed stream 7; CO₂-depleted ODH reactor effluent stream 20)can be characterized by an ethane concentration of less than about 5 mol%, less than about 4 mol %, less than about 3 mol %, less than about 2mol %, or less than about 1 mol %; from about 0.1 mol % to about 5 mol%, from about 0.1 mol % to about 4 mol %, from about 0.1 mol % to about3 mol %, from about 0.15 mol % to about 2 mol %, or from about 0.2 mol %to about 1 mol %. In an aspect, the second reactant mixture (e.g., EOreactor feed stream 7; CO₂-depleted ODH reactor effluent stream 20) canbe characterized by an ethane concentration of less than about 3 mol %,or from about 0.1 mol % to about 3 mol %. For example, the secondreactant mixture (e.g., EO reactor feed stream 7; CO₂-depleted ODHreactor effluent stream 20) can be characterized by an ethaneconcentration of less than about 3 mol %, less than about 2 mol %, orless than about 1 mol %; from about 0.1 mol % to about 3 mol %, fromabout 0.15 mol % to about 2 mol %, or from about 0.2 mol % to about 1mol %.

In an aspect, the second reactant mixture (e.g., EO reactor feed stream7; CO₂-depleted ODH reactor effluent stream 20) can be characterized byan ethylene concentration of equal to or greater than about 15 mol %,equal to or greater than about 20 mol %, equal to or greater than about25 mol %, or equal to or greater than about 30 mol %; from about 15 mol% to about 75 mol %, from about 20 mol % to about 70 mol %, from about25 mol % to about 65 mol %, or from about 30 mol % to about 60 mol %.

In an aspect, supplemental oxygen can be introduced to the EO reactorfeed stream 7, in addition to the oxygen introduced to the EO reactor 2via the EO recycle feed stream 15 and/or via the ODH reactor effluentstream 6. In an aspect, the EO oxygen make-up feed stream 14 can beprovided to the EO reactor 2. Stream 14 can be oxygen gas, technicaloxygen (which can contain some air), air, oxygen enriched air, and thelike, or combinations thereof. In an aspect, stream 14 comprisessubstantially pure oxygen (e.g., oxygen having less than about 1 vol. %contaminants, such as nitrogen (N₂), argon (Ar), etc.). The EO oxygenmake-up feed stream 14 provides for supplemental oxygen or fresh oxygen,which replenishes the oxygen that has been consumed (e.g., via ODHreaction in reactor 1, EO reaction in EO reactor 2, combustion reactionsin reactors 1 and 2, etc.) and/or lost (e.g., via purge stream 13) inthe process.

In an aspect, a ballast gas make-up stream can be provided to the EOreactor 2. In an aspect, the ballast gas make-up stream introduced tothe EO reactor 2 comprises methane.

In an aspect, the process for producing EO as disclosed herein cancomprise introducing methane to the ODH reactor 1 (e.g., via stream 19,as displayed in the configurations of FIGS. 1-2 ) and/or the EO reactor2, wherein streams 10, 12, 13, 15, 7, 16, and 5 are characterized by amethane concentration of equal to or greater than about 20 mol %, equalto or greater than about 25 mol %, equal to or greater than about 30 mol%, equal to or greater than about 35 mol %, or equal to or greater thanabout 40 mol %; from about 20 mol % to about 80 mol %, from about 25 mol% to about 75 mol %, from about 30 mol % to about 70 mol %, from about35 mol % to about 65 mol %, or from about 40 mol % to about 60 mol %.

As will be appreciated by one of skill in the art, and with the help ofthis disclosure, ballast gases may be inert gases introduced with otherprocess feeds that build up in a recycle process. For example, argon andnitrogen may enter with the oxygen and/or ethane feeds to the ODHreactor 1 and/or EO reactor 2 and can build up to appreciableconcentrations in the recycle loop (e.g., streams 10, 12, 15, 7, 16, and5). Ballast gases may be selected for their favorable properties (e.g.,thermal performance, chemical inertness), and may also be purposelyintroduced into the recycle process (i.e., a process for producing EO asdisclosed herein). Further, and as will be appreciated by one of skillin the art, and with the help of this disclosure, excess ethane in theEO reactor 2 (i.e., ethane that is not converted in the ODH reactor 1)may also be considered a ballast gas, although it is not fully inert. Insome aspects, the ballast gas may comprise atmospheric inerts, methane,ethane, or combinations thereof. Without wishing to be limited bytheory, the concentrations of ballast gas components that areestablished in the recycle loop depend on the rate at which the ballastgas components enter into the process (i.e., feeds to the ODH reactor 1and/or EO reactor 2) and the flowrate of the purge stream 13 in whichthe ballast gas components leave the process. While ethane has beenpreviously considered for use as a primary ballast gas in processesintegrating ODH and EO, and without wishing to be limited by theory,ethane is not fully inert in the ODH reactor 1 and the EO reactor 2, soallowing ethane to accumulate in the recycle loop leads to loss ofethane due to its reaction with oxygen, which in turn depresses thechemical efficiency of the process. Advantageously, inert gases otherthan ethane may be used to share the role of ballast gas. For example,if the oxygen feed used as streams 14 and 18 contains about 0.2 mol %argon, and a purge ratio f (f=flowrate of stream 13 divided by theflowrate of streams 10 or 12) is 0.001, argon can accumulate in therecycle loop to a level of greater than about 10 mol %. As anotherexample, when methane is used as ballast gas in stream 19, at a molarflowrate equal to 1.3% of ethane feed stream 17, about 40% methaneaccumulates in the recycle loop. By employing inert gases other thanethane as the ballast gas, the concentration of ethane can be kept at areasonable level in the recycle loop, e.g., below about 20 mol %, orbelow about 10 mol %.

The EO reactor 2 can be any suitable reactor, such as a continuous flowreactor, a fixed bed reactor, a fluidized bed reactor, a multi-tubularreactor, and the like, or combinations thereof. In an aspect, the ODHreactor 1 comprises a continuous flow multi-tubular reactor, wherein thetubes contain an EO catalyst, and wherein a cooling medium contacting anouter surface of the tubes provides for temperature control of the EOreactor.

In an aspect, the EO reactor 2 can be characterized by an EO reactoroperating temperature of from about 100° C. to about 400° C., from about150° C. to about 350° C., or from about 200° C. to about 300° C. The EOreactor operating temperature is defined as the average of EO reactorinlet temperature and EO reactor outlet temperature.

In an aspect, the EO reactor 2 can be characterized by an EO reactoroperating pressure of from about 1 barg to about 35 barg, from about 3barg to about 30 barg, from about 5 barg to about 25 barg, or from about10 barg to about 20 barg.

In an aspect, the EO reactor 2 comprises an EO catalyst. The EO catalystcomprises any EO catalyst suitable for catalyzing an EO reaction. Forexample, the EO catalyst can comprise silver. In an aspect, the EOcatalyst comprises silver oxide. The EO catalyst may further comprise apromoter, such as rhenium, tungsten, molybdenum, chromium, and the like,or combinations thereof.

In an aspect, a moderator can be further introduced to the EO reactor 2.Generally, a moderator may be introduced to EO reactors comprising an EOcatalyst for catalyst performance control. Nonlimiting examples ofmoderators suitable for use in the EO reactor as disclosed hereininclude a chlorohydrocarbon, ethyl chloride, vinyl chloride,dichloroethane, ethylene dichloride, and the like, or combinationsthereof. In an aspect, the moderator comprises ethyl chloride. Themoderator may be present in the EO reactor feed stream 7 in an amount offrom about 1 part per million volume (ppmv) to about 2,000 ppmv, basedon the total volume of the EO reactor feed stream 7. The EO reactor, EOcatalyst, and EO operating conditions (e.g., pressure, temperature,moderator) are described in more detail in U.S. Pat. Nos. 8,148,555; and9,649,621; each of which is incorporated by reference herein in itsentirety.

The ethylene introduced to the EO reactor 2 contacts the EO catalystand, in the presence of oxygen, is converted to EO via the EO reaction(2):

C₂H₄+½O₂→C₂H₄O  (2)

Several side reactions (i.e., reactions other than ethylene conversionto EO via EO reaction (2)) may occur in the EO reactor 2, such as COoxidation to CO₂. Further, a portion of ethane, a portion of ethylene, aportion of acetic acid, a portion of acetylene, or combinations thereofin the EO reactor 2 can combust in the presence of oxygen to produceCO₂, and water.

The EO reactor effluent stream 8 can be recovered from the EO reactor 2,wherein the EO reactor effluent stream 8 can comprise EO, ethylene,ethane, oxygen, carbon dioxide, and water. The EO reactor effluentstream 8 can further comprise a ballast gas (e.g., methane) and/or amoderator. In an aspect, ethylene is not separated from the EO reactoreffluent stream 8; i.e., ethylene is not separated from the ethane inthe EO reactor effluent stream 8, prior to recycling the ethylene in theEO reactor effluent stream 8 to the ODH reactor 1 and EO reactor 2.

In an aspect, a process for producing EO as disclosed herein cancomprise a step of separating at least a portion of the second effluentstream (e.g., EO reactor effluent stream 8) into an EO product stream(e.g., EO product stream 9) and a recycle stream (e.g., EO-depletedproduct stream 10; CO₂-depleted stream 12); wherein the EO productstream comprises at least a portion of the EO in the second effluentstream; and wherein the recycle stream comprises ethane, ethylene, andoxygen.

In an aspect, at least a portion of the EO reactor effluent stream 8 canbe introduced to the product recovery system 3 to produce the EO productstream 9 and the EO-depleted product stream 10; wherein the EO productstream 9 comprises EO and water, and wherein the EO-depleted productstream 10 comprises ethylene, ethane, oxygen, and carbon dioxide. Theproduct recovery system 3 may employ condensation (e.g., lowering thestream temperature to promote condensation); a series of absorption andstripping columns; etc.

In some aspects, and referring to the configuration of FIG. 1 , theEO-depleted product stream 10 can be introduced to the CO₂ removalsystem 4 to yield CO₂-depleted stream 12 and CO₂-containing stream 11.The CO₂-containing stream 11 can comprise at least 25 mol %, at least 35mol %, at least 50 mol %, or at least 70 mol % of the CO₂ in theEO-depleted product stream 10. The CO₂-depleted stream 12 comprisesethylene, ethane, and oxygen; and optionally CO₂ (i.e., the CO₂ that hasnot been removed into CO₂-containing stream 11).

In an aspect, the recycle stream (e.g., EO-depleted product stream 10;CO₂-depleted stream 12) can be characterized by a combined concentrationof ethane and ethylene of less than about 60 mol %, less than about 55mol %, less than about 50 mol %, less than about 45 mol %, less thanabout 40 mol %, less than about 35 mol %, less than about 30 mol %, orless than about 25 mol %; from about 15 mol % to about 60 mol %, fromabout 15 mol % to about 55 mol %, from about 15 mol % to about 50 mol %,from about 18 mol % to about 45 mol %, from about 19 mol % to about 40mol %, from about 20 mol % to about 35 mol %, from about 20 mol % toabout 30 mol %, or from about 20 mol % to about 25 mol %.

In an aspect, the recycle stream (e.g., EO-depleted product stream 10;CO₂-depleted stream 12) can be characterized by an ethane concentrationof less than about 30 mol %, less than about 25 mol %, less than about20 mol %, less than about 15 mol %, less than about 10 mol %, less thanabout 9 mol %, less than about 8 mol %, less than about 7 mol %, lessthan about 6 mol %, less than about 5 mol %, less than about 4 mol %,less than about 3 mol %, less than about 2 mol %, or less than about 1mol %; from about 0.01 mol % to about 30 mol %, from about 0.01 mol % toabout 25 mol %, from about 0.01 mol % to about 20 mol %, from about 0.01mol % to about 15 mol %, from about 0.01 mol % to about 10 mol %, fromabout 0.02 mol % to about 9 mol %, from about 0.05 mol % to about 8 mol%, from about 0.06 mol % to about 7 mol %, from about 0.08 mol % toabout 6 mol %, from about 0.1 mol % to about 5 mol %, from about 0.1 mol% to about 4 mol %, from about 0.1 mol % to about 3 mol %, from about0.15 mol % to about 2 mol %, or from about 0.2 mol % to about 1 mol %.

In an aspect, a purge stream 13 can be withdrawn from the EO-depletedproduct stream 10 and/or the CO₂-depleted stream 12, or from any othersuitable stream in the recycle loop comprising units 1, 2, 3, and 4 inFIGS. 1-2 , to avoid build-up of inerts in the recycle loop. A purgeratio (f) is defined as the volumetric flow rate of the purge stream 13divided by the flow rate of the stream(s) it was withdrawn from (e.g.,divided by the volumetric flow rate of the EO-depleted product stream 10and/or the CO₂-depleted stream 12, respectively). In an aspect, thepurge ratio can be from about 0.0001 to about 0.005, from about 0.0002to about 0.003, or from about 0.0003 to about 0.002.

In an aspect, a process for producing EO as disclosed herein cancomprise a step of recycling a first portion of the recycle stream(e.g., EO-depleted product stream 10; CO₂-depleted stream 12) to the ODHreactor 1 (e.g., via ODH reactor feed stream 5), and a second portion ofthe recycle stream to the EO reactor 2 (e.g., via EO reactor feed stream7). In such aspect, a recycle split ratio (a) can be less than about0.9, less than about 0.8, less than about 0.7, less than about 0.6, lessthan about 0.5, less than about 0.45, less than about 0.4, less thanabout 0.35, less than about 0.3, less than about 0.25, or less thanabout 0.2, from about 0.1 to about 0.9, from about 0.2 to about 0.9,from about 0.25 to about 0.9, from about 0.2 to about 0.6, from about0.3 to about 0.6, or from about 0.25 to about 0.45; wherein the recyclesplit ratio is defined as the ratio of the volumetric flowrate of thefirst portion of the recycle stream divided by the sum of the volumetricflowrate of the first portion of the recycle stream and the volumetricflowrate of the second portion of the recycle stream. In an aspect, therecycle split ratio can be less than about 0.6; or from about 0.2 toabout 0.6.

Purge stream 13 is withdrawn from the recycle stream (e.g., EO-depletedproduct stream 10; CO₂-depleted stream 12), and the remainder of therecycle stream is split into the EO recycle feed stream 15 (e.g., asecond portion of the recycle stream) and the ODH recycle feed stream 16(e.g., a first portion of the recycle stream). As disclosed herein, theEO recycle feed stream 15 (e.g., a second portion of the recycle stream)and the ODH recycle feed stream 16 (e.g., a first portion of the recyclestream) are recycled to the EO reactor 2 and the ODH reactor 1,respectively without separating ethane from ethylene in the EO recyclefeed stream 15 and the ODH recycle feed stream 16, respectively. As willbe appreciated by one of skill in the art, and with the help of thisdisclosure, owing to relatively low conversions of ethylene in the EOreactors, processes for the production of EO generally operate at highrecycle ratios (i.e., the flowrate of EO reactor feed stream is about25-50 times the flowrate of fresh ethylene (in the case of a stand-aloneEO process) or fresh ethane (in the case of an EO process integratedwith ODH)), and thus conventional processes may separate the ethane fromethylene for recycling purposes. However, the process for producing EOas disclosed herein advantageously excludes the separation of ethanefrom ethylene from recycle streams (e.g., EO-depleted product stream 10;CO₂-depleted stream 12; EO recycle feed stream 15; ODH recycle feedstream 16).

In an aspect, a process for producing EO as disclosed herein canadvantageously display improvements in one or more processcharacteristics when compared to conventional processes for theproduction of EO.

In an aspect, the EO in the EO product stream 9 can be further used as achemical intermediate, for example for conversion to ethylene glycol andits derivatives.

In an aspect, a process for producing EO as disclosed herein can employoperating conditions for both the ODH and EO reactors that can beadvantageously selected to optimize process performance. The EO reactor2 may be operated with similar conditions (e.g., feed composition,pressure, inlet temperature, and coolant temperature) and similar design(e.g., including choice of catalyst) as in conventional EO processes.Alternatively, the EO reactor 2 may be operated at a different ethyleneconcentration in the inlet; for example, instead of the conventionalconcentration of 30-35% ethylene in the feed, somewhat lower ethyleneconcentrations, e.g., of 15-30%, or 15-25% may be advantageouslyemployed in the EO reactor feed stream 7 under certain circumstances.The operating conditions for the ODH reactor 1 may be selected to ensureprocess safety (which imposes a limit on the inlet concentration ofoxygen, as well as the inlet and coolant temperatures) while maximizingreactor performance and optimizing reactor size. In an aspect, both theODH reactor 1 and the EO reactor 2 can be operated with oxygenconcentrations in their respective feed close to their maximumrespective safe values, by advantageously maintaining separate oxygenmake-up flows to each reactor.

In an aspect, as the recycle flow to the ODH reactor 1 decreases, andassuming the oxygen concentration in the ODH feed is maintained at themaximum safe level to avoid flammable conditions, the fractionalconversion of oxygen through the ODH reactor 1 must increase in order toconvert the required amount of ethane (i.e., close to the amount offresh ethane fed to the ODH reactor 1). The ODH reactor may beadvantageously operated at an oxygen conversion greater than about 30%,greater than about 45%, or greater than about 60%; from about 30% toabout 100%, from about 45% to about 100%, from about 45% to about 99%,or from about 60% to about 97.5%.

In an aspect, a process for producing EO as disclosed herein canadvantageously provide for adjusting the concentration of ethylene inthe recycle loop by adjusting the recycle split ratio. For example, theconcentration of ethylene in the recycle loop may be adjusted upward byincreasing the recycle split ratio, and downward by decreasing therecycle split ratio. The ability to adjust the concentration of ethylenein the recycle loop by adjusting the recycle split ratio advantageouslyprovides a measure of control that can be used to optimize the processfor producing EO as disclosed herein, which control measure is notavailable in conventional process configurations that lack the splitrecycle concept. This control measure may be used in conjunction withcontrolling the purge ratio and the flow of make-up ballast gas, toestablish reactor feed compositions most conducive to high processperformance (e.g., process productivity and/or selectivity).

In an aspect, a process for producing EO as disclosed herein cancomprise a step of determining a molar concentration of ethylene in therecycle stream. For purposes of the disclosure herein, the step ofdetermining a molar concentration of ethylene in the recycle streamencompasses determining the molar concentration of ethylene at anysuitable point in the recycle loop (e.g., streams 10, 12, 13, 15, 7, 16,and 5); such as determining the ethylene concentration in stream 10,stream 12, stream 13, stream 15, stream 7, stream 16, stream 5, and thelike, or combinations thereof. For example, a process analyzer mayprovide continuous or periodic analysis of the recycle streamcomposition, or the composition of the feed to the EO reactor 2.

In an aspect, a process for producing EO as disclosed herein cancomprise a step of comparing the molar concentration of ethylene in therecycle stream with a target molar concentration of ethylene in therecycle stream. Responsive to the step of comparing the molarconcentration of ethylene in the recycle stream with a target molarconcentration of ethylene in the recycle stream, when the molarconcentration of ethylene in the recycle stream is less than the targetmolar concentration of ethylene in the recycle stream, the recycle splitratio can be increased. In other words, if the concentration of ethylenein the recycle stream is below the value at which the most favorableprocess performance is attained, the recycle split ratio can beincreased. Responsive to the step of comparing the molar concentrationof ethylene in the recycle stream with a target molar concentration ofethylene in the recycle stream, when the molar concentration of ethylenein the recycle stream is greater than the target molar concentration ofethylene in the recycle stream, the recycle split ratio can bedecreased. In other words, if the concentration of ethylene in therecycle stream is above the value at which the most favorable processperformance is attained, the recycle split ratio can be decreased. In anaspect, the recycle split ratio can be modified to be in a range of fromabout 0.2 to about 0.8, or from about 0.2 to about 0.6.

In an aspect, the target molar concentration of ethylene in the recyclestream can be from about 25 mol % to about 40 mol %, from about 27 mol %to about 37 mol %, or from about 30 mol % to about 35 mol %.

In an aspect, a process for producing EO as disclosed herein can beadvantageously characterized by an amount of EO in the EO product stream9 that is greater than an amount of EO produced in an otherwise similarprocess that is characterized by a molar concentration of ethylene inthe recycle stream different than the target molar concentration ofethylene in the recycle stream of from about 25 mol % to about 40 mol %(e.g., below 25 mol % or above 40 mol %).

In some aspects, adjusting the recycle split ratio, and depending on theconfiguration of process equipment, may involve incrementally opening orclosing a flow control valve, or adjusting the operating parameters of arecycle compressor. The results from the same process analysis may alsobe used to adjust the purge flow rate (for example, to increase purgeflow rate when the concentration of atmospheric inerts becomes higherthan desired) and/or the makeup ballast gas flow rate (for example, todecrease the makeup ballast gas flow rate when the concentration of theballast gas, e.g. methane, exceeds the desired value).

In an aspect, a process for producing EO as disclosed herein can employODH catalysts, EO catalysts, and moderators as previously describedherein. Without wishing to be limited by theory, ideally, the ODHcatalyst in the ODH reactor 1 would only act on ethane, and would notconvert ethylene; and likewise, under ideal assumptions, the EO catalystin the EO reactor 2 would only act on ethylene, and would not convertethane. In reality, some small fractional conversion of these compounds(ethylene in the ODH reactor 1; ethane in the EO reactor 2) may takeplace over the catalysts employed; and these fractional conversions maybe referred to as “parasitic” conversions, which are the result ofparasitic reactions (e.g., unwanted reactions). The process forproducing EO as disclosed herein advantageously gives rise to relativelylow-level parasitic conversions, which in turn leads to improved processcharacteristics (e.g., relatively high EO yield). As will be describedin more detail in the Examples later herein, relatively low-levelparasitic conversions can be accomplished by minimizing theconcentration of ethane in the recycle streams and/or by selecting anappropriately low value of the recycle split to the ODH reactor 1. In anaspect, a process for producing EO as disclosed herein canadvantageously provide for reducing the operating cost of the ODHreactor 1.

In an aspect, a process for producing EO as disclosed herein canadvantageously provide for a relatively high ethylene oxide yield, whilebalancing the competing objective of low equipment cost. Ethylene oxideyield (defined as the molar fraction of the fresh feed of ethane that isconverted (in the sequence of ODH and EO reactors) to the EO product) isthe most important parameter affecting the operating cost of EOproduction. The practical value (as opposed to the theoretical value) issmaller than 100%, owing to imperfect selectivity towards desiredproducts in the ODH and EO reactors, ethane and ethylene losses in purgestream(s), and in some cases parasitic conversion of ethane in the EOreactor and/or ethylene in the ODH reactor. In a process integrating ODHand EO for EO production, such as the process for producing EO asdisclosed herein, the cost of ODH and EO reactors can represent a largefraction of the equipment cost, since expensive cryogenic separation ofethylene from ethane in the recycle loop is advantageously avoided. Inan aspect, a process for producing EO as disclosed herein canadvantageously provide for optimizing reactor size and cost. Additionaladvantages of the process for producing EO as disclosed herein can beapparent to one of skill in the art viewing this disclosure.

EXAMPLES

The subject matter having been generally described, the followingexamples are given as particular embodiments of the disclosure and todemonstrate the practice and advantages thereof. It is understood thatthe examples are given by way of illustration and are not intended tolimit the specification of the claims to follow in any manner.

Example

The data encompass novel process configurations for integrating ODH andEO as examined by process and reactor modeling and simulation. Theintegrated ODH and EO process was modeled using Aspen Plus processsimulation software, based on the EO production system 100 displayed inFIG. 1 . The ODH reactor was characterized by an ethylene carbon molarselectivity of 95%, a CO carbon molar selectivity of 2.5%, and a CO₂carbon molar selectivity of 2.5%. An upper limit concentration of 8.5%oxygen was imposed on the feed to the ODH reactor to avoid explosiveconditions. The ODH reactor was modeled as a multi-tubular packed bedreactor in which the conversion of ethane was selected to achieve massbalance of ethane (i.e., the rate of conversion of ethane in the ODHreactor plus losses of ethane elsewhere in the system matched the feedrate of fresh ethane). The EO reactor was characterized by an ethyleneoxide carbon molar selectivity of 84% and a CO₂ carbon molar selectivityof 16%. The oxygen concentration in the feed to the EO reactor wasmaintained at 9.1%, and the oxygen conversion was taken to be 30% in theEO reactor, representative of conventional EO processes. The model alsoaccounted for conversion of 50% of the CO in the EO reactor feed to CO₂.To allow for meaningful comparison among cases studied, the ethyleneconcentration in the EO reactor feed was maintained at 34.5% for allcases (by selecting appropriate values for the free parameters). Therecovery of EO from the EO reactor effluent was modeled as 100%efficient, while 40% CO₂ removal efficiency was modeled for the CO₂removal unit. The ethane feed stream was taken to be 100% ethane, whilethe oxygen feed contained 0.2% argon. When make-up ballast gas wasincluded in the calculations, methane was used as makeup ballast gas;parameter b represents the ballast gas make-up molar flowrate divided bythe molar flowrate of the fresh ethane feed stream. The modelcalculations were conducted for several combinations of the processparameters (purge ratio f; recycle split ratio a; ballast gas make-upb). The calculations were performed using assumptions of idealchemistry, and also using small assumed losses of ethane and/or ethylenedue to their parasitic conversion. Parameter z_(C2H6) represents thefractional conversion of ethane in the EO reactor, to form combustionproducts CO₂ and water. Parameter z_(C2H4) represents the fractionalconversion of ethylene in the ODH reactor, to form combustion productsCO₂ and water. The results (Examples 1-14b) are shown in Table 1 below,in which the EO yield Y_(EO) is the molar flowrate of EO in the EOproduct stream divided by the molar flowrate of the fresh ethane feedstream; the EO recycle ratio RR_(EO) is the molar flowrate of the EOreactor feed stream divided by the molar flowrate of ethane in the freshethane feed stream; and the ODH recycle ratio RR_(ODH) is the molarflowrate of the ODH reactor feed stream divided by the molar flowrate ofethane in the fresh ethane feed stream. The conversion of oxygen throughthe ODH reactor (x_(O2,ODH)) and the mole fraction of ethylene in the EOreactor feed (y_(C2H4,EOin)) are also shown in Table 1.

TABLE 1 Example # z_(C2H4) z_(C2H6) f_(purge) a b Y_(EO) RR_(ODH)RR_(EO) x_(O2, ODH) y_(C2H4, EOin) 1 0 0 0.003 0.282 0 0.737 8.92 28.9779.0% 34.5% 2 0 0 0.001 0.277 0 0.776 9.20 30.48 79.0% 34.5% 3 0 00.0003 0.275 0 0.790 9.30 31.05 79.0% 34.5% 4 0 0 0.001 0.278 0.01370.786 9.33 30.86 79.0% 34.5% 5 0 0 0.001 0.214 0.0135 0.786 7.44 30.8799.0% 34.5% 6 0 0 0.001 0.391 0.0135 0.785 12.69 30.86 58.0% 34.5% 7 0 00.001 0.669 0.0135 0.785 21.01 30.85 35.0% 34.5% 8 0 0 0.001 0.989 0.0140.785 30.64 30.84 24.0% 34.5% 9 0.01 0 0.001 0.286 0.0135 0.763 9.3329.98 79.0% 34.5% 10  0.01 0 0.001 0.990 0.0112 0.713 27.79 28.01 26.5%34.5% 11  0 0.01 0.001 0.274 0 0.698 8.28 27.42 79.0% 34.5% 12  0 0.010.001 0.277 0.0135 0.781 9.27 30.68 79.0% 34.5% 13  0 0.01 0.001 0.9800.0135 0.778 30.11 30.56 24.2% 34.5% 14  0.01 0.01 0.001 0.286 0.01250.757 9.26 29.77 79.0% 34.5% 15  0.01 0.01 0.001 0.990 0.011 0.707 27.5827.79 26.5% 34.5% 14a 0.01 0.01 0.001 0.285 0.0125 0.756 9.20 29.6979.0% 32.3% 14b 0.01 0.01 0.001 0.287 0.0125 0.760 9.31 29.86 79.0%36.3%

The maximum value of EO yield, given the selectivities to ethylene andEO in the two reactors, is 0.798. Examples 1-3 in Table 1 show that thismaximum selectivity value may be approached in the case where ethane isnot parasitically converted in the process, by selecting a very lowvalue of the purge ratio f. The accumulation of atmospheric inerts andother contaminants in the recycle loop, which may affect reactoroperation, poses practical limitations on reducing the purge ratio. An fvalue of 0.001 is consistent with current industrial practice, and istherefore used in further examples. Thus, operating without on-purposemethane as ballast gas results in Example 2 with an EO yield of 0.776, afew percent below the maximum value; wherein the yield loss can beattributed to purge losses. Example 4 shows that the yield can beimproved by introducing methane as a ballast gas, thereby suppressingthe concentration of ethane in the recycle loop.

Examples 4-8 demonstrate that if no adverse chemistry occurs (z_(C2H4)and z_(C2H6) are zero), high yields may be attained at different valuesof parameter a, ranging from a small fractional recycle (a=0.29) tonearly full recycle to the ODH reactor (a=0.99). However, the magnitudeof the ODH recycle ratio RR_(ODH) increases as a increases, and becomesquite large at full recycle; a reactor built to accommodate thecorresponding high flowrate would be large compared to the reactor for aprocess with smaller value of a, so it is beneficial to select a valuefor a that is lower than one. As the value of a decreases, thefractional conversion of oxygen through the ODH reactor increases.Practical values for a range from a maximum of 1 to a minimum set by theneed to convert sufficient ethane in the ODH reactor to meet processperformance. For the process conditions modeled here, this minimum valuefor a is 0.22; at this value, the conversion of oxygen through the ODHreactor is complete. The economic optimum is not necessarily obtained atthe minimum value for a; other considerations, such as reactionkinetics, also affect the equipment cost. In practice, intermediatevalues of a, for example from 0.25 to 0.9, or from 0.3 to 0.6, mayresult in the economically most attractive process.

Examples 9 and 10 demonstrate that the effect of parasitic conversion ofethylene in the ODH reactor on EO yield is much greater for full recycle(large a value) than for minimal recycle (small a value), which providesfurther incentive to reduce the recycle split ratio to a value wellbelow one.

Example 11 demonstrates that even a small parasitic conversion of ethanein the EO reactor can significantly affect the EO yield if no measuresare taken to suppress the concentration of ethane in the recycle loop.Examples 12 and 13 illustrate that the introduction of methane asballast gas greatly reduces the EO yield loss; and the same could beaccomplished with a lower purge rate, by allowing more argon to build upin the recycle loop.

Examples 14 and 15 demonstrate that even when both ethane and ethyleneare lost to parasitic conversion in the reactors, the extent of EO yieldloss can be limited to a reasonable level if a sufficiently small valueof a is selected, along with values of b and f_(purge) suitable to limitethane accumulation in the recycle loop.

Examples 14a and 14b, in conjunction with Example 14, show how a slightadjustment of the recycle split ratio results in a corresponding changein the ethylene mole fraction in the EO reactor feed. This demonstrateshow the recycle split ratio may be used to control the composition ofethylene in the recycle loop to its desired value. It should be notedthat the results in the examples correspond to steady-state operation;in industrial practice, the response will be a dynamic one, such thatthe loop concentrations gradually approach the desired value. A thoroughunderstanding of the process dynamics, such as may be gained fromprocess simulation, will aid in configuring a stable and dependablecontrol scheme. In examples 14, 14a, and 14b, the fractional conversionof oxygen in the ODH reactor is assumed to stay the same as the flowthrough the ODH reactor is varied. This might be achieved in practicethrough slight adjustments to the reactor operating temperature by anysuitable means. Alternatively, the fractional oxygen conversion can beleft to find its own new steady-state value at the same reactorconditions; and in this case, the response factor (fractional change inethylene concentration divided by fractional change in recycle splitratio) will be smaller, but still positive, so the control scheme can besuccessful in this case as well.

In conclusion, these results demonstrate that, even in the absence of acostly ethylene/ethane separation step in the recycle process, and evenif undesired process chemistry leads to parasitic loss of ethane and/orethylene, very good process performance can be attained, with EO yieldsonly marginally lower than the maximum EO yield—but only by carrying outthe process with a recycle split ratio at a suitably low value, e.g.less than 0.6, less than 0.45, or less than 0.3; or from about 0.2 toabout 0.6; and/or oxygen conversions through the ODH reactor of greaterthan 30%, greater than 45%, or greater than 60%; from about 30% to about100%, from about 45% to about 100%, from about 45% to about 99%, or fromabout 60% to about 97.5%. Such high conversions are not obvious; theselective oxidation of ethylene to EO (carried out in a similar type ofreactor with similar operating conditions), for example, is commonlycarried out with ethylene conversion levels much smaller than 30%.Moreover, the results in Table 1 show how the composition of the EOreactor feed can be suitably adjusted to the desired value by varyingthe recycle split ratio during operation.

The results in Table 1 surprisingly display that the ODH reactor processdoes not require as large a recycle ratio as the EO process, even thoughboth reactors are selective partial oxidation reactors operating atsimilar temperature and pressure ranges with similar concentrations ofoxygen in the feed. For example, an ODH recycle ratio (ratio of stream16 to stream 5) of 8-20 may suffice. Advantageously, the recycle splitratio a can be selected to operate the ODH reactor with desiredperformance, without requiring an excessively large reactor. In someaspects, the recycle split ratio may be advantageously set at a value inthe range from 0.25 to 0.9, or from 0.3 to 0.6.

Additional Disclosure

A first embodiment, which is an ethylene oxide (EO) production processcomprising: (a) introducing a first reactant mixture to a first reactorto produce a first effluent stream; wherein the first reactant mixturecomprises ethane, and oxygen; and wherein the first effluent streamcomprises ethylene, ethane, and oxygen; (b) introducing a secondreactant mixture to a second reactor to produce a second effluentstream; wherein the second reactant mixture comprises at least a portionof the first effluent stream; wherein ethylene is not separated from thefirst effluent stream; and wherein the second effluent stream comprisesEO, ethane, ethylene, and oxygen; (c) separating at least a portion ofthe second effluent stream into an EO product stream and a recyclestream; wherein the EO product stream comprises at least a portion ofthe EO in the second effluent stream; and wherein the recycle streamcomprises ethane, ethylene, and oxygen; and (d) recycling a firstportion of the recycle stream to the first reactor in step (a), and asecond portion of the recycle stream to the second reactor in step (b);wherein ethylene is not separated from the recycle stream; wherein arecycle split ratio is from about 0.2 to about 0.6; and wherein therecycle split ratio is defined as the ratio of the volumetric flowrateof the first portion of the recycle stream divided by the sum of thevolumetric flowrate of the first portion of the recycle stream and thevolumetric flowrate of the second portion of the recycle stream.

A second embodiment, which is the process of the first embodiment,wherein the first reactor is characterized by an oxygen conversion offrom about 30% to about 100%.

A third embodiment, which is the process of any of the first and thesecond embodiments, wherein the first effluent stream is characterizedby an ethane concentration of from about 0.1 mol % to about 5 mol %.

A fourth embodiment, which is the process of any of the first throughthe third embodiments, wherein the recycle stream is characterized by anethane concentration of from about 0.1 mol % to about 5 mol %.

A fifth embodiment, which is the process of any of the first through thefourth embodiments, wherein a concentration of ethane in the secondreactant mixture and/or the recycle stream is from about 0.1 mol % toabout 3 mol %.

A sixth embodiment, which is the process of any of the first through thefifth embodiments further comprising withdrawing a third portion of therecycle stream as a purge stream; wherein the purge stream ischaracterized by a purge ratio of from about 0.0001 to about 0.005; andwherein the purge ratio is defined as the ratio of the volumetricflowrate of the purge stream divided by the volumetric flowrate of therecycle stream.

A seventh embodiment, which is the process of any of the first throughthe sixth embodiments further comprising introducing methane to thefirst reactor and/or the second reactor, wherein the recycle stream ischaracterized by a methane concentration of from about 20 mol % to about80 mol %.

An eighth embodiment, which is the process of any of the first throughthe seventh embodiments, wherein the recycle stream is characterized bya combined concentration of ethane and ethylene from about 15 mol % toabout 50 mol %.

A ninth embodiment, which is the process of any of the first through theeighth embodiments, wherein supplemental oxygen is introduced to thefirst reaction mixture, in addition to the oxygen recycled to the firstreactor via the first portion of the recycle stream.

A tenth embodiment, which is the process of any of the first through theninth embodiments, wherein supplemental oxygen is introduced to thesecond reaction mixture, in addition to the oxygen introduced to thesecond reactor via the second portion of the recycle stream and/or viathe first effluent stream.

An eleventh embodiment, which is the process of any of the first throughthe tenth embodiments, wherein the recycle split ratio is less thanabout 0.45.

A twelfth embodiment, which is the process of any of the first throughthe eleventh embodiments, wherein the recycle split ratio is less thanabout 0.3.

A thirteenth embodiment, which is the process of any of the firstthrough the twelfth embodiments, wherein the first reactor ischaracterized by an ethane conversion of from about 60% to about 100%.

A fourteenth embodiment, which is the process of any of the firstthrough the thirteenth embodiments, wherein the first reactant mixtureis characterized by a molar ratio of ethylene to ethane of from about1.3 to about 3.0.

A fifteenth embodiment, which is the process of any of the first throughthe fourteenth embodiments, wherein the first effluent stream, thesecond effluent stream, and the recycle stream comprise carbon dioxide;and wherein (i) at least a portion of the carbon dioxide is removed fromthe first effluent stream prior to feeding the first effluent stream tothe second reactor in step (b); and/or (ii) at least a portion of thecarbon dioxide is removed from the recycle stream prior to the step (d)of recycling a first portion of the recycle stream to the first reactorin step (a), and a second portion of the recycle stream to the secondreactor in step (b).

A sixteenth embodiment, which is an ethylene oxide (EO) productionprocess comprising: (a) introducing a first reactant mixture to anoxidative dehydrogenation (ODH) reactor to produce a first effluentstream; wherein the first reactant mixture comprises ethane, and oxygen;and wherein the first effluent stream comprises ethylene, ethane, andoxygen; (b) introducing a second reactant mixture to an EO reactor toproduce a second effluent stream; wherein the second reactant mixturecomprises at least a portion of the first effluent stream; whereinethylene is not separated from the first effluent stream; and whereinthe second effluent stream comprises EO, ethane, ethylene, oxygen, andcarbon dioxide; (c) separating at least a portion of the second effluentstream into an EO product stream and a recycle stream; wherein the EOproduct stream comprises at least a portion of the EO in the secondeffluent stream; wherein the recycle stream comprises ethane, ethylene,oxygen, and carbon dioxide; and wherein at least a portion of the carbondioxide is optionally removed from the recycle stream; (d) recycling afirst portion of the recycle stream to the ODH reactor in step (a), anda second portion of the recycle stream to the EO reactor in step (b);wherein ethylene is not separated from the recycle stream; wherein arecycle split ratio is defined as the ratio of the volumetric flowrateof the first portion of the recycle stream divided by the sum of thevolumetric flowrate of the first portion of the recycle stream and thevolumetric flowrate of the second portion of the recycle stream; (e)determining a molar concentration of ethylene in the recycle stream; (f)comparing the molar concentration of ethylene in the recycle stream witha target molar concentration of ethylene in the recycle stream; (g)responsive to step (f), when the molar concentration of ethylene in therecycle stream is less than the target molar concentration of ethylenein the recycle stream, increasing the recycle split ratio; and (h)responsive to step (f), when the molar concentration of ethylene in therecycle stream is greater than the target molar concentration ofethylene in the recycle stream, decreasing the recycle split ratio.

A seventeenth embodiment, which is the process of the sixteenthembodiment, wherein the target molar concentration of ethylene in therecycle stream is from about 25 mol % to about 40 mol %.

An eighteenth embodiment, which is the process of any of the sixteenthand the seventeenth embodiments, wherein a concentration of ethane inthe second reactant mixture and/or the recycle stream is from about 0.1mol % to about 3 mol %.

A nineteenth embodiment, which is the process of any of the sixteenththrough the eighteenth embodiments, wherein the ODH reactor ischaracterized by an ethane conversion of from about 70% to about 100%.

A twentieth embodiment, which is the process of any of the sixteenththrough the nineteenth embodiments, wherein the recycle split ratio ismodified to be in a range of from about 0.2 to about 0.6.

For the purpose of any U.S. national stage filing from this application,all publications and patents mentioned in this disclosure areincorporated herein by reference in their entireties, for the purpose ofdescribing and disclosing the constructs and methodologies described inthose publications, which might be used in connection with the methodsof this disclosure. Any publications and patents discussed herein areprovided solely for their disclosure prior to the filing date of thepresent application. Nothing herein is to be construed as an admissionthat the inventors are not entitled to antedate such disclosure byvirtue of prior invention.

In any application before the United States Patent and Trademark Office,the Abstract of this application is provided for the purpose ofsatisfying the requirements of 37 C.F.R. § 1.72 and the purpose statedin 37 C.F.R. § 1.72(b) “to enable the United States Patent and TrademarkOffice and the public generally to determine quickly from a cursoryinspection the nature and gist of the technical disclosure.” Therefore,the Abstract of this application is not intended to be used to construethe scope of the claims or to limit the scope of the subject matter thatis disclosed herein. Moreover, any headings that can be employed hereinare also not intended to be used to construe the scope of the claims orto limit the scope of the subject matter that is disclosed herein. Anyuse of the past tense to describe an example otherwise indicated asconstructive or prophetic is not intended to reflect that theconstructive or prophetic example has actually been carried out.

While embodiments of the disclosure have been shown and described,modifications thereof can be made without departing from the spirit andteachings of the invention. The embodiments and examples describedherein are exemplary only, and are not intended to be limiting. Manyvariations and modifications of the invention disclosed herein arepossible and are within the scope of the invention.

Accordingly, the scope of protection is not limited by the descriptionset out above but is only limited by the claims which follow, that scopeincluding all equivalents of the subject matter of the claims. Each andevery claim is incorporated into the specification as an embodiment ofthe present invention. Thus, the claims are a further description andare an addition to the detailed description of the present invention.The disclosures of all patents, patent applications, and publicationscited herein are hereby incorporated by reference.

What is claimed is:
 1. An ethylene oxide (EO) production processcomprising: (a) introducing a first reactant mixture to a first reactorto produce a first effluent stream; wherein the first reactant mixturecomprises ethane, and oxygen; and wherein the first effluent streamcomprises ethylene, ethane, and oxygen; (b) introducing a secondreactant mixture to a second reactor to produce a second effluentstream; wherein the second reactant mixture comprises at least a portionof the first effluent stream; wherein ethylene is not separated from thefirst effluent stream; and wherein the second effluent stream comprisesEO, ethane, ethylene, and oxygen; (c) separating at least a portion ofthe second effluent stream into an EO product stream and a recyclestream; wherein the EO product stream comprises at least a portion ofthe EO in the second effluent stream; and wherein the recycle streamcomprises ethane, ethylene, and oxygen; and (d) recycling a firstportion of the recycle stream to the first reactor in step (a), and asecond portion of the recycle stream to the second reactor in step (b);wherein ethylene is not separated from the recycle stream; wherein arecycle split ratio is from about 0.2 to about 0.6; and wherein therecycle split ratio is defined as the ratio of the volumetric flowrateof the first portion of the recycle stream divided by the sum of thevolumetric flowrate of the first portion of the recycle stream and thevolumetric flowrate of the second portion of the recycle stream.
 2. Theprocess of claim 1, wherein the first reactor is characterized by anoxygen conversion of from about 30% to about 100%.
 3. The process ofclaim 1, wherein the first effluent stream is characterized by an ethaneconcentration of from about 0.1 mol % to about 5 mol %.
 4. The processof claim 1, wherein the recycle stream is characterized by an ethaneconcentration of from about 0.1 mol % to about 5 mol %.
 5. The processof claim 1, wherein a concentration of ethane in the second reactantmixture and/or the recycle stream is from about 0.1 mol % to about 3 mol%.
 6. The process of claim 1 further comprising withdrawing a thirdportion of the recycle stream as a purge stream; wherein the purgestream is characterized by a purge ratio of from about 0.0001 to about0.005; and wherein the purge ratio is defined as the ratio of thevolumetric flowrate of the purge stream divided by the volumetricflowrate of the recycle stream.
 7. The process of claim 1 furthercomprising introducing methane to the first reactor and/or the secondreactor, wherein the recycle stream is characterized by a methaneconcentration of from about 20 mol % to about 80 mol %.
 8. The processof claim 1, wherein the recycle stream is characterized by a combinedconcentration of ethane and ethylene from about 15 mol % to about 50 mol%.
 9. The process of claim 1, wherein supplemental oxygen is introducedto the first reaction mixture, in addition to the oxygen recycled to thefirst reactor via the first portion of the recycle stream.
 10. Theprocess of claim 1, wherein supplemental oxygen is introduced to thesecond reaction mixture, in addition to the oxygen introduced to thesecond reactor via the second portion of the recycle stream and/or viathe first effluent stream.
 11. The process of claim 1, wherein therecycle split ratio is less than about 0.45.
 12. The process of claim 1,wherein the recycle split ratio is less than about 0.3.
 13. The processof claim 1, wherein the first reactor is characterized by an ethaneconversion of from about 60% to about 100%.
 14. The process of claim 1,wherein the first reactant mixture is characterized by a molar ratio ofethylene to ethane of from about 1.3 to about 3.0.
 15. The process ofclaim 1, wherein the first effluent stream, the second effluent stream,and the recycle stream comprise carbon dioxide; and wherein (i) at leasta portion of the carbon dioxide is removed from the first effluentstream prior to feeding the first effluent stream to the second reactorin step (b); and/or (ii) at least a portion of the carbon dioxide isremoved from the recycle stream prior to the step (d) of recycling afirst portion of the recycle stream to the first reactor in step (a),and a second portion of the recycle stream to the second reactor in step(b).
 16. An ethylene oxide (EO) production process comprising: (a)introducing a first reactant mixture to an oxidative dehydrogenation(ODH) reactor to produce a first effluent stream; wherein the firstreactant mixture comprises ethane, and oxygen; and wherein the firsteffluent stream comprises ethylene, ethane, and oxygen; (b) introducinga second reactant mixture to an EO reactor to produce a second effluentstream; wherein the second reactant mixture comprises at least a portionof the first effluent stream; wherein ethylene is not separated from thefirst effluent stream; and wherein the second effluent stream comprisesEO, ethane, ethylene, oxygen, and carbon dioxide; (c) separating atleast a portion of the second effluent stream into an EO product streamand a recycle stream; wherein the EO product stream comprises at least aportion of the EO in the second effluent stream; wherein the recyclestream comprises ethane, ethylene, oxygen, and carbon dioxide; andwherein at least a portion of the carbon dioxide is optionally removedfrom the recycle stream; (d) recycling a first portion of the recyclestream to the ODH reactor in step (a), and a second portion of therecycle stream to the EO reactor in step (b); wherein ethylene is notseparated from the recycle stream; wherein a recycle split ratio isdefined as the ratio of the volumetric flowrate of the first portion ofthe recycle stream divided by the sum of the volumetric flowrate of thefirst portion of the recycle stream and the volumetric flowrate of thesecond portion of the recycle stream; (e) determining a molarconcentration of ethylene in the recycle stream; (f) comparing the molarconcentration of ethylene in the recycle stream with a target molarconcentration of ethylene in the recycle stream; (g) responsive to step(f), when the molar concentration of ethylene in the recycle stream isless than the target molar concentration of ethylene in the recyclestream, increasing the recycle split ratio; and (h) responsive to step(f), when the molar concentration of ethylene in the recycle stream isgreater than the target molar concentration of ethylene in the recyclestream, decreasing the recycle split ratio.
 17. The process of claim 16,wherein the target molar concentration of ethylene in the recycle streamis from about 25 mol % to about 40 mol %.
 18. The process of claim 16,wherein a concentration of ethane in the second reactant mixture and/orthe recycle stream is from about 0.1 mol % to about 3 mol %.
 19. Theprocess of claim 16, wherein the ODH reactor is characterized by anethane conversion of from about 70% to about 100%.
 20. The process ofclaim 16, wherein the recycle split ratio is modified to be in a rangeof from about 0.2 to about 0.6.